This invention relates to an oil filter comprising a filter housing, a removable cover and a filter element which is arranged in the filter housing.
German Utility Model No. DE-GM 94 11 212.6 discloses a liquid filter, particularly for use as an oil filter for combustion engines. The disclosed liquid filter comprises a filter housing with, in each case, at least one liquid inlet channel and one liquid outlet channel, additionally, a detachable cover which closes the filter housing in a liquid-tight manner as well as a filter insert that can be removed from the filter housing and can be exchanged separately. Unlike a screw-on replacement filter which may only be replaced in its entirety, this liquid filter is screwed together with the combustion engine via a connecting flange. Screw-on replacement filters have been known for many years and have come into widespread use, primarily with internal combustion engines of motor vehicles. Every time such a screw-on replacement filter has to be replaced, it can only be disposed of and recycled in its entirety, thus resulting in considerable material costs. With the filter arrangement disclosed in the aforementioned German Utility Model, the material costs may be reduced by merely exchanging the filter insert and by re-using the remaining components of the liquid filter. One drawback of this known filter arrangement is that, when the filter insert is unscrewed, the oil inside the filter housing flows out and dirties the filter housing and the cover, as well as further structural parts situated in the engine compartment. For that reason, the German Utility Model proposes to arrange a discharge screw at the lowest point of the filter housing. When the filter insert is replaced, the discharge screw is first opened so that oil situated in the housing can flow out. Then the cover can be opened, and afterwards it is possible to remove the filter element. This handling, however, is extremely impractical. In addition, there is a danger that leakage problems may occur in the vicinity of the discharge screw, thus resulting in a loss of oil.